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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Monday
• 
• High: 81 °
• Low: 50 °
• Chance of T-Storms

• Tuesday
• 
• High: 68 °
• Low: 48 °
• Partly Cloudy

• Wednesday
• 
• High: 73 °
• Low: 54 °
• Clear

• Thursday
• 
• High: 79 °
• Low: 63 °
• Partly Cloudy

• Friday
• 
• High: 91 °
• Low: 64 °
• Chance of T-Storms

Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
117 PM EDT Monday may 21 2012 


Aviation... 


//discussion... 


The passage of a weak cold front will be the main concern for 
aviation interests during the afternoon through evening. Surface 
heating has been plentiful enough during the morning to lend 
confidence on the chance of thunderstorms in the Detroit area during 
the middle afternoon. Light Post frontal showers will linger through 
middle evening across the rest of the region with some MVFR ceiling. 
The MVFR conditions will then improve during the night as northerly 
flow deepens and high pressure carries dry air in from the west. 
Upstream observational evidence over the upper Midwest strongly 
supports the clearing trend with a cautious eye toward Southern Lake 
Huron for possible lake induced stratocu that could filter into the 
Detroit area around sunrise Tuesday morning. Otherwise, VFR 
conditions are expected for Tuesday with diminishing northerly wind 
through the day. 


For dtw...plentiful surface heating has slowed the passage of an 
already slowly moving cold front. This has allowed enough 
instability to form for increased thunderstorm potential at the 
Airport. Best estimate is 19-21z with activity moving off the 
northeast shortly thereafter to be replaced by light rain and MVFR 
ceiling through about middle evening. 


//Dtw threshold threats... 


* high confidence in ceiling below 5000 feet during the late 
afternoon through evening. 


* Moderate confidence in timing and coverage of thunderstorms 
this afternoon. 


&& 


Previous discussion...issued 1157 am EDT Monday may 21 2012 


Update... 


A narrow window of opportunity remains for surface based 
convective development during the afternoon along the wind shift 
and out ahead of the Post frontal band of light showers that has 
been on radar all morning. Severe weather potential remains very 
limited by rather a modest cape/shear profile advertised in the 
12z NAM off of the 12z DTX sounding. High resolution model output 
does indicate clusters of convection developing during peak 
heating after 0-1km mean layer cape builds to around 1000 j/kg 
with a generous estimate of 0-6km bulk shear of 25 knots. The Post 
frontal band of light showers represents the region of best upper 
support provided by the middle level trough axis with a bit cooler 
temperatures aloft under entrance region of weak upper jet. This 
forcing is expected to help touch off the surface based convection 
as the afternoon wears on with both then lasting through middle 
evening. The earlier forecast update maintained the 
chance/scattered forecast for showers and thunderstorms with an 
eye toward the afternoon package for refinement of higher probability of precipitation 
into the evening hours. The strongest storms will be capable of 
small hail and gusty winds with heavy downpours being the main 
concern due to slow storm motion and slow eastward progression of 
the front. 


Previous discussion...issued 250 am EDT Monday may 21 2012 


Short term...today and tonight 


Surface front is expected to push into the area this morning as wave 
lifts north along this boundary into the northern Great Lakes and 
Canada. Existing showers/thunderstorms will likely diminish to some 
extent during the first half of the day due to diurnal minimum for 
instability and also the loss of lift/forcing with the exiting wave. 


A second wave will lift north along this boundary later today...and 
stall the surface front for a short time this afternoon and evening. 
Will maintain current pop configuration with shower/thunderstorm 
chances in the 40-50% area. The western extent of late day activity 
will be mainly determined by frontal position by that time. Given 
mesoscale boundaries oozing east out of current convection...current 
idea of limiting best chance of convection to the far eastern County Warning Area 
for round two this afternoon/evening seems in line. 


With a decided lack of upper level support and with modest 
instability at best...severe weather is not expected. However...the 
slow movement of this front...and any storms along it...will bring a 
chance of locally heavy downpours. Convective activity should pretty 
much be over by midnight as the trough axis pushes east of the area. 


Temperatures will cool down to some extent today...ranging from 
about 70 over the Saginaw Valley in behind the cold front to about 
80 along the far eastern County Warning Area...where warm sector will slowly be 
shoved east by front during the afternoon. Cooler air will then 
continue to filter into the area into tonight bringing minimum 
temperatures in the 40s to lower 50s from northwest to southeast 
across southeast lower Michigan. 


Long term...Tuesday through Sunday 


Temperatures will hold near normal on Tuesday as highs reach the 
upper 60s to around 70 degrees with the thermal trough positioned 
overhead. With some dependence on how much rain falls over the area 
on Monday, steep low level lapse rates may be supportive for some 
flat afternoon cumulus development on Tuesday afternoon underneath increasing 
subsidence and building heights aloft. Surface high pressure will 
then build into the area for the middle-week period allowing 
temperatures to rebound into the 70s and eventually 80s as a strong 
east Pacific jet begins to drive an amplification of the pattern for 
the end of the week. The building ridge over the central United 
States and Great Lakes region will provide several opportunities for 
some very warm days Thursday through Sunday with the typical 
dependence on cloud cover/convective potential. The best chance for 
any kind of organized precipitation looks to be Friday as an amplifying 
wave lifts through the northern Great Lakes and the associated cold 
front shifts through the area. However, the model consensus 
continues to keep the bulk of the forcing associated with this 
system well to our north. Forecast highs from Thursday Onward range 
from the middle 70s to the low 80s for most locations along with warm 
overnight lows hovering around 60f. 


Marine... 


There will be a chance for showers and thunderstorms into this 
evening as a cold front advances slowly across the region. Wind 
directions will uniformly turn west to northwesterly behind this 
cold front by this evening. The system will continue its weakening 
trend as it crosses the area today. Therefore...the wind field is 
expected to remain modest with northwesterlies possibly attaining 
15-20 knots. Surface high pressure is then forecasted to build over 
the Great Lakes region during the middle of the week. 


&& 


DTX watches/warnings/advisories... 


Michigan...none. 
Lake Huron...none. 
Lake St Clair...none. 
Michigan waters of Lake Erie...none. 


&& 


$$ 


Aviation.....Bt 
update.......bt 
short term...dg 
long term....jvc 
marine.......dg 




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at www.Weather.Gov/Detroit (all lower case).